Two types of AMR:

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1.AMR or AMR_NB ( AMR narrow band) - Mono channels ( 8 bit audio)

2.AMR_WB ( AMR wide band) - stereo channels ( 16 bit audio)

we are using AMR_NB ;

Every AMR file begins with following Hex start codes:

23 21 41 4d 52 0a ( Equal string is: #!AMR.)

if we open the amr file, without these start codes means it will display like

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Error

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Error -2048: Couldn't open the file Quotes.amr because it is not a file that QuickTime understands.

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OK

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Every audio frame is having one byte frame header;

format is as follows:

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F ( 1 bit) | FT( 4 bits) | 1 ( 1bit)

---------------------------------------------

Frame Type	Mode	Frame Size(Including 1 byte header)
0	AMR 4.75	13
1	AMR 5.15	14
2	AMR 5.9	16
3	AMR 6.7	18
4	AMR 7.4	20
5	AMR 7.95	21
6	AMR 10.2	27
7	AMR 12.2	32

if we have a file with 12.2 kbps means, we can check this by the frame header;

and moreover we can note that every frame have 1 byte header;But it is same as start. Assume that first frame's header is 3C then every frame must begins with header start code ;

if the header is having proper start code and the next it will check whether every frame is having same header info; otherwise it will reports the error as follows:

"Quicktime media file is having incorrect duration"

I have to do one more check;

if every frame is having different header start code whether the QuickTime play that AMR file ?...

3C is a frame header for first frame;

38 is a frame header for second frame;

Both frame headers indicate the same Frame Type;

whether it will works ?

Result :

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it works fine;

Test case 2:

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Instead of 0x38, I inserted the 0x20.

Then I didnt get any sound while playing it in QuickTime player and moreover the Quicktime is not giving any errors;

Instead of 0x20, I made it as 0x20, then I faced the same problem.

Every AMR frame is having 20 ms of data;

So if 40 frames are available means

40 * 20 = 800 milli seconds( play time of that frames);

1000 milliseconds = 1 second